On Earth, the most important source of hydrogen is, without contest, water, which covers more than 70% of its surface. Separating the components of the water molecule is one way of producing hydrogen.
The water molecule (H2O) is composed of two hydrogen atoms (H) and one oxygen (O) atom. To produce hydrogen, it is necessary to break down the bonds in this molecule. There are various processes for doing so, using an electric current or a series of chemical reactions.
In water electrolysis, the H2O molecule is submitted to an electric current that splits it into oxygen and hydrogen gas. This method is generally used to produce low volumes of hydrogen or to produce it near power sources at a low cost (hydroelectricity).
Currently, a great deal of research is focused on improving the output of water electrolysis. One possible avenue of improvement is electrolysis using high temperature steam.
This technology does not directly produce CO2. However, it is indispensable to factor the CO2 released during the production of electricity into the global assessment of the carbon footprint.
Thermochemical cycles bring into play the phenomenon of the decomposition of water into hydrogen and oxygen, which occurs spontaneously at very high temperature. This decomposition can be achieved at lower temperatures using chemical reaction cycles.
This hydrogen production process is currently in the research phase. It is expected to enable the production of hydrogen while limiting the release of greenhouse gases.